Radiation therapy is widely performed on patients with breast tissue affected, for example, with cancerous cells and following breast conserving surgery. The acute toxicity, long-term side effects, and cosmetic outcome of such treatment are attributable to a number of factors including technical aspects of surgery, pre-existing systemic medical conditions, the use of specific chemotherapeutic agents and administration of such relative to delivery of radiation therapy, radiation therapy treatment technique, and patient morphology. Patient morphology is generally the most difficult factor to compensate for in seeking optimum delivery of radiation therapy and a factor which most directly affects cosmetic outcome.
Optimal radiotherapy technique is described as 4500-5000 cGy to the whole breast over a period of 4.5-5 weeks, followed by a boost to the excisional biopsy site with an additional 1000-1500 cGy. The technical aspects of delivering radiation therapy as a part of breast conserving therapy are less well defined and have evolved as a function of technical innovation and studies examining the patterns of failure. Improvements in methods for field matching, the abandonment of routine regional nodal irradiation, controversies concerning the necessity and method for boost treatment, sequencing of chemotherapy, and indications for radiation therapy, have distracted the radiation oncologist from attempting technical improvements in the delivery of radiation therapy.
Treatment simulation and set-up are carried out primarily with the patient in the supine position, although certain cancer centers continue to use the decubitus position as their standard treatment position. When patients with large breasts are encountered, the decubitus position is sometimes used as an alternative to the supine position. While the supine position is considered more reproducible, it irradiates more lung and requires the use of wedge filters, high energy radiation beams, and bolus to overcome non-homogeneous dose distributions and skin overdose. The decubitus technique is performed with the breast tissue compressed to an even thickness of 6-8 cm and results in a more homogeneous dose distribution. The decubitus technique requires meticulous positioning and protection of the contralateral breast; it is therefore considered less reproducible and lacks the flexibility of supine position treatment, especially when nodal irradiation is considered. For these reasons, the decubitus technique is seldom used and has dropped from favor.
Women with large and/or pendulous breasts, or women with small to medium size breasts and unusual chest wall contours, have relatively large medial to lateral separations. The separation is defined as the measure transverse distance across the base of the breast which will require radiation therapy. Such patients require modifications and alterations to traditional treatment techniques. When treatment is carried out in the supine position, the transverse displacement of breast tissue over the anterior chest wall creates a large separation. This separation, combined with potential folding of the breast at its most caudal extent, are two of the aspects of breast radiation therapy that contribute to non-uniformity of dose distributions and irradiation of large volumes of lung and heart tissue. A number of technical modifications have been proposed to improve the dose distribution in women with large separations. These modifications include the use of wedge filters, high-energy photon beams, beam-spoilers and bolus but which do not entirely or satisfactorily overcome the above described disadvantages and dangers.
As mentioned, an alternative method of administering such therapy is to have the patient fully reclined in the decubitus position upon a horizontal surface and to position the radiation energy source adjacent the surface of tissue to be treated. Because this method does not physically isolate the part to be treated by radiation, it has the serious disadvantage of irradiation of tissue other than the affected portion of the breast and further including heart, lung and skin tissue proximate to the breast, all resulting from the patient being in the decubitus position. These and other associated problems are especially acute in patients with large breasts and/or pulmonary or cardiac conditions to whom scattered and excessive radiation creates significant risks.